track whether we have an active writer, which can be approximated by: is the write lock unavailable

src/StackExchange.Redis/ExceptionFactory.cs

@@ -229,10 +229,11 @@ void add(string lk, string sk, string v)
             // Add server data, if we have it
             if (server != null)
             {
-                server.GetOutstandingCount(message.Command, out int inst, out int qs, out long @in, out int qu, out long toRead, out long toWrite);
+                server.GetOutstandingCount(message.Command, out int inst, out int qs, out long @in, out int qu, out bool aw, out long toRead, out long toWrite);
                 add("OpsSinceLastHeartbeat", "inst", inst.ToString());
                 add("Queue-Awaiting-Write", "qu", qu.ToString());
                 add("Queue-Awaiting-Response", "qs", qs.ToString());
+                add("Active-Writer", "aw", aw.ToString());
 
                 if (@in >= 0) add("Inbound-Bytes", "in", @in.ToString());
                 if (toRead >= 0) add("Inbound-Pipe-Bytes", "in-pipe", toRead.ToString());

src/StackExchange.Redis/PhysicalBridge.cs

@@ -289,13 +289,14 @@ private void ShutdownSubscriptionQueue()
         internal bool TryEnqueueBackgroundSubscriptionWrite(in PendingSubscriptionState state)
             => isDisposed ? false : (_subscriptionBackgroundQueue ?? GetSubscriptionQueue()).Writer.TryWrite(state);
 
-        internal void GetOutstandingCount(out int inst, out int qs, out long @in, out int qu, out long toRead, out long toWrite)
+        internal void GetOutstandingCount(out int inst, out int qs, out long @in, out int qu, out bool aw, out long toRead, out long toWrite)
         {
             inst = (int)(Interlocked.Read(ref operationCount) - Interlocked.Read(ref profileLastLog));
             lock(_backlog)
             {
                 qu = _backlog.Count;
             }
+            aw = !_singleWriterMutex.IsAvailable;
             var tmp = physical;
             if (tmp == null)
             {

src/StackExchange.Redis/ServerEndPoint.cs

@@ -375,17 +375,18 @@ internal ServerCounters GetCounters()
             return counters;
         }
 
-        internal void GetOutstandingCount(RedisCommand command, out int inst, out int qs, out long @in, out int qu, out long toRead, out long toWrite)
+        internal void GetOutstandingCount(RedisCommand command, out int inst, out int qs, out long @in, out int qu, out bool aw, out long toRead, out long toWrite)
         {
             var bridge = GetBridge(command, false);
             if (bridge == null)
             {
                 inst = qs = qu = 0;
                 @in = toRead = toWrite = 0;
+                aw = false;
             }
             else
             {
-                bridge.GetOutstandingCount(out inst, out qs, out @in, out qu, out toRead, out toWrite);
+                bridge.GetOutstandingCount(out inst, out qs, out @in, out qu, out aw, out toRead, out toWrite);
             }
         }
 

src/StackExchange.Redis/StackExchange.Redis.csproj

@@ -15,7 +15,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Pipelines.Sockets.Unofficial" Version="2.0.9" />
+    <PackageReference Include="Pipelines.Sockets.Unofficial" Version="2.0.10" />
     <PackageReference Include="System.Diagnostics.PerformanceCounter" Version="4.5.0" />
     <PackageReference Include="System.IO.Pipelines" Version="4.5.1" />
     <PackageReference Include="System.Threading.Channels" Version="4.5.0" />